Issue Averaging Array

Hello all, I have a project I am working on, and I am so close to finishing. Unfortunately this last bit has snagged me. Using this code, it appears that instead of actually adding each numerical value together, it is adding each new value to the end of the string. thus 5+8=58 ect... I would appreciate any pointers.

Below is the javascript code, and I have attached all of the files used in the application

[code]var score_list = [];var full_list = [];

var $ = function (id) { return document.getElementById(id);}

var add_click = function () { var last = $("last_name").value var first = $("first_name").value var score1 = $("score_input").value score_list.push(score1); full_list.push(last + ", " + first + ": " + score1); update_full_list(); // Beginning of issue var Sum = 0 var Average // Find the lowest & highest for (var i = 0; i < score_list.length; i++) { Sum=Sum + score_list[i] //as i understand it, this should be adding all of the array up in one value instead of just stringing them together Average = Sum/score_list.length } alert(Sum); // I used this to show me what value it was getting for sum, and it displays the strung together numbers instead of the sum I want//end test code